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US 5,479,131 AGranted
Squid array voltage standard
AssigneeHewlett-Packard Company
InventorGregory S. Lee
Life of this patent
Estimating the term…
Abstract
A Josephson junction voltage standard based on rf controlled dc SQUID's is proposed. A microwave signal is injected using rf control lines. A D/A converter based on series-connected rf controlled SQUID's is described.
Claims9
A circuit for supplying a voltage standard comprising:
- at least one array of at least two SQUID's connected in series between two nodes;
- each of said SQUID's including two Josephson junctions connected in parallel, an inductor and damping resistors, said Josephson junctions and said inductor connected in a superconducting loop, said two damping resistors each connected in parallel with each said Josephson junction thereby shunting each said Josephson junction;
- means for applying dc bias current between the two nodes to the array so that a dc bias current flows constantly through each of the SQUID's in the array and so that the same current flows simultaneously through each of the SQUID's in the array;
- means for magnetically coupling an rf control signal having a frequency to each of said SQUID's, in order to apply a control flux to each of the at least two SQUID's, thereby causing an output voltage across the two nodes, said output voltage serving as the voltage standard, wherein said magnetic coupling means includes:
- two control lines;
- and
- intermediate magnetic coupling means including a plurality of loops, each loop comprising at least two pairs of inductors, one pair magnetically coupling the loop to the two control lines and the other pair magnetically coupling the loop to some of the sequentially connected SQUID's in the array;
- said two control lines being 180.degree. out of phase with each other so that the magnetic flux coupled with each said SQUID is twice that provided by a single control line.
5 more elements
A method for supplying a voltage standard comprising:
- providing one or more SQUID's connected between two nodes, each of said SQUID's including two Josephson junctions connected in parallel, an inductor and damping resistors, said Josephson junctions and said inductor connected in a superconducting loop, said two damping resistors each connected in parallel with each said Josephson junction thereby shunting each said Josephson junction;
- applying a dc bias current between the two nodes;
- and
- magnetically coupling an rf control signal having a frequency to each of said SQUID's, in order to apply a control flux to each of the SQUID's, the amplitude of said rf control signal being selected such that the rf control signal causes a predetermined integer number n flux quantum transitions per junction per cycle of each of the SQUID's, thereby causing an output voltage across the two nodes, said output voltage serving as a voltage standard and standard said voltage being proportional to the frequency of the rf control signal f and to n;
- wherein said coupling step applies to each of the SQUID's a dc offset flux so that when n is even, then the d.c. offset in the control flux is 0 modulo .PHI..sub.0, and when n is odd, the d.c. offset in the control flux is .PHI..sub.0 /2 modulo .PHI..sub.0, .PHI..sub.0 being the flux quantum h/2e, where h is the Planck's constant and e the charge of an electron.
2 more elements
A circuit for supplying a voltage standard comprising:
- one or more SQUID's connected between two nodes, each of said SQUID's including two Josephson junctions connected in parallel, an inductor and damping resistors, said Josephson junctions and said inductor connected in a superconducting loop, said two damping resistors each connected in parallel with each said Josephson junction thereby shunting each said Josephson junction;
- means for applying a dc bias current between the two nodes;
- and
- means for magnetically coupling an rf control signal having a frequency to each of said SQUID's, in order to apply a control flux to each of the SQUID's, the amplitude of said rf control signal being selected such that the rf control signal causes a predetermined integer number n flux quantum transitions per junction per cycle of each of the SQUID's, thereby causing an output voltage across the two nodes, said output voltage serving as a voltage standard and said standard voltage being proportional to the frequency of the rf control signal f and to n;
- wherein said coupling means applies to each of the SQUID's a dc offset flux so that when n is even, then the d.c. offset in the control flux is 0 modulo .PHI..sub.0, and when n is odd, the d.c. offset in the control flux is .PHI..sub.0 /2 modulo .PHI..sub.0, .PHI..sub.0 being the flux quantum h/2e, where h is the Planck's constant and e the charge of an electron.
2 more elements
Dependencies are inferred from the claim text.